The present invention relates to a bag for containing two separate substances that are to be mixed.
Though, hereinafter, specific reference is made to a bag containing two different fluids to be mixed, the present invention also applies to a bag containing a fluid and a powder, granulated substance, or any other mixing substance, typically for pharmaceutical use.
As is well known, there are many substances in the medical field that have to be used simultaneously with each other or actually mixed together in order to obtain the desired therapeutic and/or diagnostic effects, but that cannot be mixed prior to the moment of use since they would then lose all or at least some of their efficacy or would otherwise undergo undesirable changes.
A typical example is bags containing a solution for dialysis, replacement or infusion purposes containing calcium salts and bicarbonate which, if mixed before being packed, during high-temperature sterilisation, react to form insoluble calcium carbonate which cannot then be infused into the patient.
To solve this problem, tubular plastic bags have been proposed containing two or more chambers separate from each other, generally by means of weld lines. Between each pair of chambers there is also a communication channel or hole which is sealed by a breakable valve which when suitably flexed or compressed by the user breaks, allowing the liquids inside to move between the chambers and mix together.
This solution does however have drawbacks which have greatly limited its use. In the first place, this bag requires long mixing times, and proper mixing of the liquids in the respective chambers cannot be achieved. This is because the liquids can only migrate through the communication channels or holes, and the cross section of these is limited. Consequently only a small amount of liquid per unit time manages to pass from one chamber to the other, and a fairly considerable amount of time is needed to allow all the liquid in one chamber to pass into another. In addition to this it is not always possible to transfer all the liquid from one chamber into another in a single pass, owing to the capacity of the other chamber, and it then becomes necessary to pour the liquid in both directions some number of times before mixing is complete. As these processes have to be performed by compressing one or other chamber as appropriate, thorough mixing requires long, fatiguing manipulations; often, therefore, the operator will cut these short with mixing still incomplete and the liquids not yet uniformly mixed, and the concentration of the various active components may therefore be left out of balance, with harmful consequences on the intended treatment.
Furthermore it is no easy matter to break the valve and this part of the operation may in some cases itself require complex and repeated manipulation of the bag by the user, making the whole liquid mixing process problematical.
To solve this problem, another suggestion already made has been to separate the various chambers by means of weak weld lines, that is lines in which the weld is made "lighter" so that the weld breaks when pressure is applied to at least one chamber. However, this solution is also unsatisfactory: the weak weld is very difficult to make as it requires great attention to welding times and parameters to avoid making either an inadequate weld (which will not guarantee the separation of the liquids in the different chambers) or too strong a weld (which could result in the bag itself breaking or other welds coming apart, for example along the edges of the bag, and liquid escaping).
Still more significantly, when the weld is being broken fragments or particles of the weak weld may come loose from the bag and contaminate the liquid, which would thereby be seriously compromised.